Process for the recovery of benzol and its homologues from solvents



NOV. 6, 1934. O SCHGNEBQRN 1,980,009

PROCESS FOR THE RECOVERY OF BENZOL AND ITS HOMOLOGUES FROM SOLVENTS Filed Sept. 11, 1931 Patented Nov. 6, 1934 ITE STATES PATENT OFFICE PROCESS FOR THE RECOVERY OF BENZOL AND ITS HOMOLOGUES FROM .SOL-

VENTS Heinrich Schiineborn,

Kettwig-Ruhr, Germany,

assignor, by mesne assignments, to The Koppers vCompany of Delaware, Pittsburgh, Pa, a corporation of Delaware I Application September 11, 1931, Serial No. 562,299

In Germany September 12, 1930 4 Claims.

- My inventionrelates to the recovery of-hydrocarbons for instance benzol and'its homologues from solvents which contain also hydrogen sulphide in free or combined state for instance from wash oils used for the removal of benzol and its homologues from coal distillation gases and more particularly to the recovery of benzol and its homologues from said solvents or wash 7 oils whereby the benzol and its homologues are p, it has been completely freed in the still from benzol, and preferably after it has been precooled'in a heat exchanger, for example with cooled solvent containing benzol, into direct contact with cold water. This arrangement was, however, later abandoned as the cooling water at low temperatures required in cooling the solvent for further use in absorption of benzol from gas easily became emulsive with the solvent when in direct contact with the solvent, the capacity of saidsolvent for taking up benzol being thus considerably reduced. Latterly in order to avoid such disadvantages, it was decided to cool indirectly the hot solvent coming from either the benzol still or from the heat exchanger, for instance by means of a tubular cooler. In this way, it is true, any formation of an emulsion of the water with the wash oil was avoided, but other considerable dimculties result in connection with same, as'the metal parts of the still and the cooling device are dangerously corroded so that frequently it was necessary to carry out repairs'to plants used in the benzol recovery processesof this kind. I

Now the object of my present invention is to provide aproces's'for the recovery of benzol from the solvents as indicated, in such a way that neither an emulsion of thewater nor any damage or anychemical attack occurs on the metal parts of the washing apparatus of the still and (or) of the-cooling contrivance which serves for carrying out'the' process. I'have found that the heavy corrosion of the distilling and cooling arrangements which are used in old benzol recovery plants, was efiected by'c'ertain salts and more especially by chloride ofammonium'and sulphide of ammonium, which compounds for instance come from the coal dise tillation gas in case the benzol was removed in a so-called semi-direct or direct process from the gas. These compounds are dissolved in the solvent or wash oil, since the usual wash oils practically always contain a certain small amount of water, generally of 0.10.8%.

According to my invention, the solvent of the wash oil containing sulphate of ammonium, chloride of ammonium and similar salts of a corroding and soluble nature, after it is drawn off from the contrivance serving for the distilling of the benzol and its homologues and preferably after it has been cooled as usual in a heat exchanger, is washed With water at a temperature above the temperature at which an emulsion of water with the oil will not occur and afterwards the purified solvent is cooled down in a suitable indirect cooler for instance a tubular cooler to the temperature which is necessary for the reuse of the solvent. By this treatment practically the entire contents of any soluble salts giving rise to corrosion is removed out of the solvent before the latter comes into contact with the metal parts of the indirect cooler.

A further object of my invention, is to provide an improved contrivance for carrying out the process herein described.

With these and other objects of the invention in view I will now describe the nature of the present invention on the lines of the accompanying drawing, which shows a side view and a partial vertical longitudinal section of a contrivance constructed according to my invention.

The contrivance shown on the drawing, may serve for instance to distill off benzol and its homologues from awash oil used for washing the benzol and its homologues out of the coal distillation gas. The contrivance comprises a customary distilling column 2 provided with a number of shelves 1. To this distilling column the oils to be treated are fed. through a siphon like bend pipe line 3 from a heater, the function of which will be discussed later. The wash oil entering into the column 2 flows through same from the top to the bottom and thus comes into contact with steam which is introduced into the lower part of the column by the pipe line 4. 0n the way through the column the benzol and the volatile homologues are driven out of the wash oil, said products finally leaving the column through the pipe line 5 at its upper end which is connected up with a condensing contrivance not shown, however, on the drawing for condensing the vapours escaping from the wash oil.

In the lower part of the column 2, the wash oil collects in the course of the process practically freed from any volatile hydrocarbons. The height of the level of the oil on the column bottom can be tested by an oil register pipe 6 made of glass or the like. The foot of the column 2 is connected up by two pipe lines '7 and 8 with a device 9 provided with an overflow pipe 10, the height of which is so measured that the oil in the bottom department of column 2 is kept at the de sired height. The oil flows into the overflow contrivance 9 through the pipe line '7, whereas the pipe line 3 serves for balancing the pressure of the overflow column 2 with the overflow contrivance.

In the device 9 the wash oil freed from the benzol and its homologues fiows oil to the heat exchanger 12 through the pipe line 11. In same the hot wash oil passes over several tubular coils through which cold wash oil containing benzol and its homologues flow. The cold wash oil is led through the pipe line 13 to the heat exchanger and leaves same by the pipe line 14 which is connected up with the oil preheater 15. This oil preheater is fitted up with a heating coil 16 through which hot steam is passed. In the oil preheater the oil is brought up to the necessary initial temperature required for carrying out the distillation in the column 2, which is connected up with the preheater 15 at its upper end by means of the above mentioned siphon pipe 3 and by the pressure balancing pipe 17 through which the vapour arising from the heating of the wash oil can escape without disturbing theuniform flow of the oil from the oil preheater 15. I

From the preheater exchanger 12 the hot washing oil proceeds by the pipe line 18 to the washer 19 which is fitted with a row of perforated sieve bottoms 20 fitted at the one end with a bent upwards projection 21 acting as a weir.

In the washing contrivance 19 the wash oil is washed with any suitable liquids, preferably wa-- ter at such a temperature which does not permit the forming of an emulsion of the water with the oil. 'The washing liquid is for this purpose heated up to the required temperature in an overhead tank 22 fitted with a heating coil 23 for passing through steam. To the tank 22 fresh liquid is supplied by-the pipe line 24. Continuously or intermittently the preheated washing liquid is drawn oil from the tank 22 by the pipe line 26 controlled bya valve 25. The washer is also provided in its lower part with a steam coil 2'? through which in case of need steam can be passed in order to keep the liquid in the washer 19 up to the desired temperature.

The washing liquid, in the case of the construction shown on the drawing, flows through the washer 19 from above downward, it is arrested on each of the horizontal sieves and thereby is distributed repeatedly over the entire section of the washer 19, thus bringing about a rain like spraying of the liquid inside the washer 19. The oil to be washed flows through the spaces between the various sieves, follows 7 therefore a zig-zag path through the washer and comes there-by into intimate contact with the washing liquid in the washer. The washing liquid collects finally in the lower part of the washer 19 and from there it is carried oif by the pipe 29 leading to the over-- how device 28. The overflow 28 is of similar construction to the overflow device 9. In the same degree, as the washing liquid is supplied to the washing contrivance said liquid flows off through the overflow 28 into the draw-off pipe line 30,

which, if desired, is connected up with the pipe line 24 of the overhead tank 22, in case the washing liquid is to be reused in a. cycle for the washing of the oil.

The wash oil to be treated after having passed through the spaces between the sieve floors is passed off at the upper end of the washing contrivance 19 through the pipe line 31 and reaches then a tubular cooler 32 through the tubes of which the oil flows. The outside of the tubes which as usually consists of metal for instance copper, is sprayed with a cooling liquid preferably water which is supplied'by the pipe line 33 to a distributor 34 from where the cooling liquid is sprayed in a rain-like form onto the cooling tubes of the cooler. The cooling liquid collects on the bottom of the cooler in a tank 35 from which it is pumped up by means of the pump 36 through the pipe line 37 to the upper end of a usual liquid cooler 38. In this cooler the heated cooling liquid being brought into contact with air is cooled down to the temperature required for cooling the wash oil. The cooled liquid finds an outlet on the bottom of the cooler 38 and it returns through the pipe line 33 to the oil cooler 32.

The wash oil cooled in the contrivance 32 reaches finally through the tube 89 the storage tank 40.

The working of the contrivance shown on the drawing is, as given below, on the presumption that a wash oil containing benzol and homologues is to be treated, the emulsion of which with water takes place at about 30 C. V

The distilling column 2 is then heated up in such a manner that the Washing oil flows off from the contrivance 2 with a temperature at about 120. In the heat exchanger 12 the wash oil is cooled down to a temperatureof -80 and is then washed directly in the washer 19 with water at about 50, in such a manner that the temperature of the oil on leaving the washer stands at about 50-55. Thereupon, the wash oil is cooled down in the indirect cooling arrangement 32 to a temperature of about 25-30. At this temperature the wash oil is ready again to be used for the further absorption of benzol and its homologues. i

The contrivance offers special advantages in cases where the conditions as regards the waste water do not allow the cooling water to be run off but requires that the cooling water be reused completely in a cycle i. e. the cooling water after passing through the cooler 32 must be cooled down and reused. In such cases the corrosive salts in the course of the process are enriched when working in the way which was formerly customary. However, by means of the process according to my invention, these corrosive salts are continuously removed from the wash oil by being washed with water. The corrosive salts are thereby continually extracted from the wash oil and correspondingly the unavoidable content of corrosive salts in the solvent and the cooling liquid is kept below that amount, where corrosion of the cooler can take place.

In the case of the construction shown on the drawing, the washer 19 is so formed that in same an oil of a lower specific gravity than water is treated. It is, of course, also possible to make the washer 19 of such a form that a wash oil of a higher specific gravity than water can be treated in same. In this case, however, the pipe line 18a shown by dashes on the drawing must be connected up with the inlet pipe 26 and the overfiow pipe 28 by a pipe line 30a'with the pipe line 31 leading to the tubular cooler 32, and the pipe branches through which the wash oil in the case of the construction shown in the drawing fiows to and from the washer must be connected with the washing liquid inlet and outlet so that the washing liquid and oil flow oppositely to their flow shown herein in full lines and must be introduced and drawn off respectively.

The inventionas hereinabove set forth is embodied in a particular form, but may be variously embodied within the scope of the claims hereinafter made.

I claim:

1. In a process of reconditioning a wash-oil solvent previously used for washing hydrocarbons, such as benzol and its homologues, from coal distillation gas for further use in removing hydrocarbons from gas as aforesaid, which process comprises distilling the wash-oil to remove the hydrocarbons absorbed during the previous washing of the gas, pre-cooling the distilled wash-oil by indirect heat exchange with wash-oil on its way to be distilled as aforesaid, and thereafter finally cooling the pre-cooled wash-oil by indirect heat exchange, as with water, to the temperature required for again washing coal gas as aforesaid, the improvement which comprises: washing the distilled wash-oil after the aforesaid distillation and precooling thereof but before the aforesaid indirect heat exchange final cooling thereof with water adapted to dissolve the soluble corrosive salt therefrom, effecting said washing of the solvent at a temperature high enough to prevent emulsification of the washing water and solvent, and separating the washing water from the solvent prior to the aforesaid final cooling thereof.

2. In a process of reconditioning a wash-oil solvent previously used for washing hydrocarbons, such as benzol and its homologues, from coal distillation gas for further use in removing hydrocarbons from gas as aforesaid, which process comprises distilling the wash-oil to remove the hydrocarbons absorbed during the previous washing of the gas and thereafter finally cooling the precooled wash-oil by indirect heat exchange, as with water, to the temperature required for again washing coal gas as aforesaid, the improvement which comprises: washing the distilled wash-oil after the aforesaid distillation thereof but before the aforesaid indirect heat exchange final cooling thereof with water adapted to dissolve the soluble corrosive salt therefrom, effecting said washing of the solvent at a temperature high enough to prevent emulsification of the washing water and solvent, and separating the washing water from the solvent prior to the aforesaid final cooling thereof.

3. In a process of reconditioning a wash-oil solvent previously used for washing hydrocarbons, such as benzol and its homologues, from coal distillation gas for further use in removing hydrocarbons from gas as aforesaid, which process comprises distilling the wash-oil to remove the hydrocarbons absorbed during the previous washing of the gas, pre-cooling the distilled wash-oil by indirect heat exchange with wash-oil on its way to be distilled as aforesaid, and thereafter finally cooling the pre-cooled wash-oil by indirect heat exchange, as with water, to the temperature required for again washing coal gas as aforesaid, the improvement which comprises: washing the distilled wash-oil after the aforesaid distillation and pre-cooling thereof but before the aforesaid indirect heat exchange final cooling thereof with water adapted to dissolve the ammonium chloride and ammonium sulphide therefrom, effecting said washing of the solvent at a temperature high enough to prevent emulsification of the washing water and solvent, and separating the washing water from the solvent prior to the aforesaid final cooling thereof.

4. In a process of reconditioning a wash-oil solvent previously used for washing hydrocarbons, such as benzol and its homologues, from coal distillation gas for further use in removing hydrocarbons from gas as aforesaid, which process comprises distilling the wash-oil to remove the hydrocarbons absorbed during the previous washing of the gas and thereafter finally cooling the precooled wash-oil by indirect heat exchange, as with water, to the temperature required for again washing coal gas as aforesaid, the improvement which comprises: washing the distilled wash-oil after the aforesaid distillation and pre-cooling thereof but before the aforesaid indirect heat exchange final cooling thereof with water adapted to dissolve the ammonium chloride and ammonium sulphide therefrom, effecting said washing of the solvent at a temperature high enough to prevent emulsification of the washing water and solvent, and separating the washing water from the solvent prior to the aforesaid final cooling thereof.

HEINRICH SCI-IONEBORN. 

